In FIG. 5, there is shown an example of a conventional rotary pump which is used for an ultrapure water pipe line in the process of manufacturing semiconductors.
Numeral 1 is a casing comprising a sucking opening 1b for sucking a main flow liquid as ultrapure water and a discharge or suction opening 1c for discharging it. Numeral 2 is an impeller which is incorporated in the casing 1.
The impeller 2 performs the function of supplying the main flow liquid from the sucking opening lb to the discharge opening 1c. A shaft 2a of the impeller 2 is secured in a cylinder 1a of the casing 1.
Numeral 6 is an annular seal member disposed between the inner surface of the cylinder 1a and the outer surface of the shaft 2a. Numeral 8 is an annular bearing disposed also between the former and the latter. Both the seal member 6 and the bearing 8 are the slidable means which are slidable on the shaft 2a of the impeller 2.
Numeral 9 is a ground seal member fixed on an end of the cylinder 1a. Numeral 10 is a motor which is combined with the shaft 2a to rotate the impeller 2.
Under such circumstances, as soon as the motor 10 is driven, the impeller 2 is rotated, thereby the main flow liquid is sucked through the sucking opening 1b and discharged from the discharge opening 1c.
On the other hand, the liquid is inclined to axially flow into a slight gap between the shaft 2a and the cylinder 1a, but its further flow is prevented by the seal member 6. As long as the pump is driven, the liquid is circulating within the casing 1 before the seal member 6.
Since the shaft 2a of the impeller 2 is rotated slidably on both the bearing 8 and the seal member 6, a slight amount of impurities or contaminants, i.e. worn matters occur from the bearing 8 and the seal member 6 respectively. The slight amount of impurities are mixed with the liquid in the interior of the casing 1. Thus, the liquid which should be ultrapure is contaminated.
For example, the purifying water to be used in the processes of manufacturing semiconductors must be of a very high purity to prevent such impurities from being adhered to the semiconductors and increase the performance of respective semiconductor products. Thus, the ultrapure water is used in the semiconductor industry.
According to such a conventional pump, the impurities that occur from the slidable portions are mixed with the ultrapure water which passes through the interior of the casing of the pump. Thus, it is contaminated by the impurities, so that the yield of the semiconductor products is reduced greatly. According to this invention, the term "impurities" means contaminants.